Retrieve the first value from a map - c++

Question

I want to retrieve the first value of speed in from the typedef struct variable which I have added into the map. Right now my code is returning all the values from the CSV file which I have read. How do I get it to return only the first value to do a comparison to get the max value from the entire column?
I have tried using map.begin()->((*it).second).speed) but it does not work.
#include <iostream>
#include <fstream>
#include <string>
#include "Date.h"
#include "Time.h"
#include <stdlib.h>
#include <map>
using namespace std;
typedef struct
{
Time t;
float speed;
int solar;
}
WindLogType;
date d;
multimap<date, WindLogType> windlog;
ifstream input , csv;
ofstream output;
string filename;
int number,choice;
string *filelist = NULL;
WindLogType T1;
int main()
{
output.open("data/met_index.txt");
cout << "Enter number of file to read : " << endl;
cin >> number ;
for(int i =0; i< number ; i++)
{
cout << "Enter File name : " << endl;
cin >> filename;
output << filename << endl;
}
filelist = new string[number];
output.close();
input.open("data/met_index.txt", ios::in);
if(!input.is_open())
{
cout<< "File not found."<<endl;
return 0;
}
else
{
string line, line2;
while(getline(input, line, '\n'))
{
//cout << line << endl;
line = "data/" + line;
for(int i =0; i<number; i++)
{
filelist[i] = line;
cout << filelist[i];
csv.open(filelist[i].c_str());
string line,sDay, sMonth, sYear, sHH, sMM;
while(getline(csv,line2, '\n' ))
{
//cout << line2 << endl;
getline(csv, sDay,'/');
getline(csv, sMonth,'/');
getline(csv, sYear,' ');
getline(csv, sHH,':');
getline(csv, sMM,',');
int day1 = atoi(sDay.c_str());
int month1 = atoi(sMonth.c_str());
int year1 = atoi(sYear.c_str());
int hour1 = atoi(sHH.c_str());
int min1 = atoi(sMM.c_str());
float s1 = 0.0;
int sr = 0;
for (int i=0; i<10; i++)
{
csv >> s1;
csv.ignore(100, ',');
}
for(int j =0; j<18; j++)
{
csv >> sr;
csv.ignore(50,',');
}
T1.t.setTime(hour1, min1);
T1.speed = s1;
T1.solar = sr;
d.setDate(day1, month1, year1);
windlog.insert(pair<date, WindLogType>(d, T1));
multimap<date, WindLogType> :: iterator it;
for(it =windlog.begin(); it!= windlog.end(); ++it)
{
int max_value = ((*it).second).speed;
if((*it).second.speed > max_value){
max_value = ((*it).second).speed;
}
cout << max_value<<endl;
}
}
csv.close();
}
/**/
}
input.close();
input.clear();
//input.open(filelist[0].c_str(), ios::in);
}
return 0;
}

Answer 1

Your are printing max_value everytime.
Move the lines that find the maximum value after you've inserted everything, i.e., after the csv.close() for example. Also, do not print the maximum while searching for it but after you've iterated over all the elements.
multimap<date, WindLogType> :: iterator it =windlog.begin();
int max_value = ((*it).second).speed;
for(++it ; it!= windlog.end(); ++it)
{
if((*it).second.speed > max_value){
max_value = ((*it).second).speed;
}
}
cout << max_value<<endl;
Of course, be sure the map is not empty.
EDIT
WindLogType.speed is a float and you're using an integer when finding the maximum, it should be float too. Probably you already know it, but since C++11 you can use the auto specifier to let the compiler deduce automatically the correct type based on the assignment expression. It is available since Visual Studio 2010 and gcc 4.4 (for gcc you have to include the --std=c++11 option).
if (!windlog.empty()) {
auto it = windlog.begin(); // 'it' is an iterator
auto max_value = it->second.speed; // you're now sure it uses the same type
for(++it; it!= windlog.end(); ++it) {
max_value = std::max(it->second.speed, max_value);
}
std::cout << max_value << std::endl;
} else {
std::cout << "Empty map" << std::endl;
}